In recent years, a touch panel is widely used in a PDA (Personal Digital Assistant) and a mobile phone. Especially, a mobile phone with a waterproof touch panel attracts attentions. A touch panel device used in this kind of mobile phone is known, for example, in Patent Document 1 and Patent Document 2. An electrostatic capacitance type touch switch device described in Patent Document 1 includes: an operational circuit which measures the variations of the resistance values of resistive electrodes and the variations of the electrostatic capacitances of switch electrodes when a finger is pressed and is not pressed on a touch switch; and a nonvolatile memory which stores the variations of the resistance values and the electrostatic capacitances, thereby preventing a malfunction due to a drop of water. A touch switch detecting device described in the Patent Document 2 uses an electrostatic capacitance type touch switch of a self-capacitance type, and sets a detection threshold as a standard to determine the presence or absence of a user operation based on the number of contact electrodes which are determined to be touched by a finger.